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Astronomi

Rabu, 27 Maret 2013

Phylogeny of North American Fireflies (Coleoptera:Lampyridae): Implications for the Evolution of Light Signals

More than 2,000 described species of fireflies live around the world,
but very little is known of their evolutionary relatedness. Of the
approximately 120 species in North America, Dr. James Lloyd at the
University of Florida has described three methods of mate attraction:
chemical signals (pheromones), glows (continuous light signals), and
flashes (short intermittent light signals).It's well known that fireflies use flashes to find members of the
same species when searching for a mate. It has been suggested this
luminescence is a carryover from the larval stage where it serves as a
warning of bad taste, and has been co-opted in many species of fireflies
as a mating signal. Although all larval fireflies produce a faint glow from paired light
organs on their eighth abdominal segment, the presence, location, shape,
and use of light organs varies greatly in adults. Only some adult
fireflies produce light; others use chemical signals for mate
attraction. In addition, only a few fireflies use a similar light organ
to the larvae — the light organ of most adult fireflies is located on
the sixth and seventh abdominal segment.In this study, the authors use a phylogenetic approach — comparing
DNA as well as morphological characteristics — to illuminate the
relationships of North American fireflies and the evolution of their
mating signals. The study included 26 species from 16 North American
genera and one species (Pterotus) that had recently been
removed from the firefly group. To test whether all the North American
fireflies evolved from a single ancestor, three European and three Asian
fireflies were also studied.The study results showed that the North American fireflies did not
evolve from a common ancestor, but different groups are closely related
to fireflies from Europe, Asia and tropical America. Further, in nine
difference instances, it was found that the use of light as a mating
signal may once have originated among fireflies and was lost.The use of short flashes independently originated among groups two to
three times. Short flashes were replaced at least once by the use of
long glows, and light signals as mating signals were lost at least three
times in the study group and replaced by pheromones as the main signal.This chart
(PDF) shows the evolutionary relationships — groups of fireflies
evolved from a common ancestor and therefore most closely related to
each other — of 16 groups or genera of North American fireflies, as well
as their method of attracting a mate: do they use a flashing signal
(FL), a constant or extended glow (EG), or chemical signals (CH)? The
fireflies that we are counting in the Firefly Watch program are the
flashing fireflies — particularly Photinus, Pyrctomena, and Photuris.